Electroacoustic transducer for use at high temperatures and pressures

ABSTRACT

An electroacoustic transducer is encased in a unitary housing, preferably machined from a single block of material, which is chemically inert, sound conducting, and sealed against moisture seepage when the transducer is immersed, under high pressure, in a hot chemical. The transducer is for immersion, as a production control sensor, in a hot corrosive fluid being chemically processed under high pressure.

United States Patent 1 [In 3,710,151

Massa et a1. 1 1 Jan. 9, 1973 [54] ELECTROACOUSTIC TRANSDUCER 3,510,698 5/1970 Massa..... ..3l0/9.1 X FOR USE AT HIGH TEMPERATURES 3,353,150 11/1967 Jacox ..340/ 3,266,011 8/1966 Massa..... 340/10 X AND PRESSURES 3,489,994 1/1970 Massa ..340/10 Inventors: Frank Massa; John F. Hubbard, 3,284,760 11/1966 Maes ..340/10 both of cohassct, Mass 3,167,668 1/1965 Nesh "340/83 X 3,113,287 12/1963 Renner ..340/9.4 X

[73] Assigneez Massa Division, Dynamics Corpora- 3,427,481 2/1969 Lenahan et all ..340/10 X tion of America, Hingham, Mass. 3,561,831 2/1971 Alibert et a1. ..310/8.3 3,573,515 2/1969 Stombaugh ..3l0/8.9 1 P116111 March 29, 1971 3,146,360 8/1964 Marshall ..310/s.9 x

[21] Appl. No.: 128,802

Primary ExammerD. F. Duggan Assistant Examiner-Mark O. Budld [52] 11.8. C1. ..3l0/8.9, 310/83, 310/9.1, Attorney-Louis Bernat 340/10 [51] Int. Cl. ..H04r 17/00 [57] ABSTRACT [58] Field of Search ..310/8.9-9.l, 9.4, A l d d 310/8 2 8 340/10 n eectroacoustic trans ucer 1S \encase 111 a unitary housing, preferably machined from a smgle block of f d material, which is chemically inert, sound conducting, [56] Re erences and sealed against moisture seepage when the trans- UNITED STATES PATENTS clucer is immersed, under high pressure, in a hot chemical. The transducer is for immersion, as 21 2,444,911 7/1948 Benioff ..340/85 production control sensor in a hot corrosive fluid 3,068,446 Ehrlich at X being chemically processed under high pressure. 3,318,578 5/1967 Branson ..310/8.9 X 3,489,932 1/1970 Kopel et a1. ..310/9.1 6 Claims, 6 Drawing Figures /l l I PATENTEDJAH 9 I975 3,710,151

FRANK MASSA JOHN F HUBBARD 8) XM QM ELECTROACOUSTIC TRANSDUCER FOR USE AT HIGH TEMPERATURES AND PRESSURES This invention relates to electroacoustic transducers and more particularly to electroacoustic transducers capable of operating in hot liquids and in environments where the hydrostatic pressure exceeds normal atmospheric pressure.

In many chemical manufacturing processes, it is necessary or desirable to control or monitor the physical properties of material undergoing processing in order to control the characteristics and uniformity in the end product. For a material in the fluid state, an important physical property is its bulk modulus of elasticity. A useful tool for controlling or monitoring the processing of such a fluid would be an instrument for directly measuring the bulk modulus of the fluid, while it is being processed during manufacture.

A means for directly measuring the bulk modulus of such a fluid measures the velocity of sound in the fluid. To provide a transducer for general application in many different chemical manufacturing processes, it is necessary for the transducer to withstand both high temperature and high ambient pressures. Additionally, the transducer should be highly reliable. It should also withstand immersion in various chemical environments without corroding, leaking, or deteriorating in performance.

Accordingly, an object of this invention is to provide an electroacoustic transducer having high reliability and operating at high temperatures and high hydrostatic pressures. Thus, one of the objects of this invention is to provide an electroacoustic transducer which may be used for generating and receiving sound in a fluid during a chemical processing thereof.

Another object is to provide a chemically inert, sound conducting, sealed housing structure surrounding a transducer element.

A further object is toprovide a one-piece outer housing which is transparent to sound and protects a transducer element in the housing from hot corrosive liquids.

This invention contemplates still other objects, features, and advantages which will become more fully ap parent from a study of the following detailed description taken in conjunction with the attached drawings, which illustrate three preferred embodiments, and in which:

FIG. 1 is a longitudinal cross-sectional view showing one illustrative embodiment of this invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view showing another illustrative embodiment of this invention;

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3;

FIG. 5 is a longitudinal cross-sectional view showing a third illustrative embodiment of this invention; and

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG 5.

In the figures, the reference character 10 identifies a housing which may be a hollow, one-piece stainless steel, shell-like body 12 having an unbroken, somewhat thimble shape. The cylindrical body and domed-shaped sealed end form the housing wall 12, which enables the housing to withstand high pressures, in excess of atmospheric pressure, without collapsing. The wall of thimble 12 is relatively thin, to enable the transmission of sound from an internal sound generating element to a fluid medium surrounding the transducer assembly.

The open end of the thimble is terminated by an integral connection section, here a threaded body section 13. Preferably, the periphery of this section has a generally hexagon shape or wrench faces to enable a wrench to be used to tighten the housing in a threaded seat. The threaded end 13 thus enables an attachment of the transducer housing 12 to the end. of a pipe or other support, for example. These threads may be sealed to a convenient structure, which enables the immersion of the mounted transducer in a tank containing the fluid being processed.

The housing 10 (including the threaded end 13) is preferably machined from a solid 'bar or block of corrosion resistant metal. Thus, there is no risk of leaking through the transducer wall. The result is a very high reliability for the structure. The threads 13 enable the one-piece housing to be attached to a mating thread at the end of a pipe of the same material. The high temperature electrical cable 21 used to drive the transducer passes through the inside of the pipe and is thus protected from exposure to the fluid medium in which the probe is immersed. Thus, a corrosion resistant probe is provided which may be immersed in a tank containing a hot corrosive fluid undergoing chemical processing.

Inside the thimble shell 12 is a transducer element 14 which is capable of converting electrical signals into mechanical vibrations. In the embodiment of FIGS. 1 and 2, this transducer element is a cylinder of polarized piezoelectric ceramic 14. This ceramic element may, for example, be made from a polarized lead zirconatetitanate material, which can be reliably operated at temperatures higher than the temperature of boiling water. It is preferable to locate the ceramic-cylinder l4 coaxial with the cylindrical body 12, which location may be achieved by the use of suitable spacers placed around the periphery of the ceramic cylinder. The spacers are not shown. The ceramic cylinder 14 has a first electrode surface 15 on its outer wall and a second electrode surface 16 on its inner wall. These electrodes may be layers of fired silver, as is usual and well known in the piezoelectric ceramic art. Electrical conductors l7 and 18 make connections from the electrodes 15 and 16 to two insulated conductors l9 and 20 inside a waterproof cable 21. The electrical connections may be made by soldering, for example.

A potting compound 22, fills the entire space between the outer wall of the ceramic cylinder 14 and the inner wall of the thimble-shaped housing wall 12. The potting compound should have a characteristic which establishes a sound transmitting path from the vibratile surface of the ceramic cylinder to the housing wall 12. For high temperature operation, the insulating materials, the polarized ceramic, and the potting compound must all be resistant to deterioration under-high temperatures. For example, we have found it possible to operate a transducer in hot liquids at temperatures in excess of 300 F. by using polarized lead zirconatetitanate for the ceramic material, teflon insulated wires, and a silicone base potting compound. If silicone rubber strips are used for the spacers between the ceramic 14 and thimble 12, they may remain imbedded in the potting compound 22 without affecting the performance of the transducer.

The construction shown in FIGS. 1 and 2 results in an omnidirectional transducer which radiates sound in all directions, lying in a plane positioned at right angles to the axis of the cylinder. This construction is ideal when it is desirable to mount the transducers side-byside, with their axes parallel. This particular configuration is used for transmitting sound from one transducer to another. For example, if two transducers are mounted side-by-side with their axes parallel, their separation distance is fixed as described and illustrated in FIG. 2 of a copending patent application of Frank Massa, Ser. No. 40,784, filed May 27, I970, entitled APPARATUS AND METHOD FOR MONITORING A CHEMICAL PROCESSING SYSTEM. The resulting structures may be employed for continuously monitoring either the sound transmission characteristics or the velocity of sound in the fluid within which they are placed.

A pair of transducers may be connected to electronic circuits for measuring the time for a sound pulse to travel from the transmitter to the receiver, and thereby provide a means for the direct measurement of the velocity of sound in the fluid, for example. A more complete description for the continuous monitoring of the velocity of sound in a fluid is given in copending application of Frank Massa and Donald P. Massa, Ser. No. 30,631, filed Apr. 22, 1970, entitled INSTRU- MENT FOR DIRECT MEASUREMENT OF THE VELOCITY OF SOUND IN A FLUID.

A modification of the construction of FIGS. 1 and 2 is illustrated in FIGS. 3 and 4. In this modified design, the general construction is similar to the construction of FIG. 1, with the exception that the ceramic cylinder 14 is replaced by the ceramic disc 23. Electrode surfaces 24 and 25 are formed on the outer and inner surfaces of the disc 23 in a manner which is well known in the art. The ceramic disc 23 is arranged with its plane face 14 positioned at right angles to the major axis of the housing structure 10, as shown in FIG. 3.

For this construction (FIG. 3) the sound is radiated through the domed end of the housing wall. There will be a concentrated narrow beam if the diameter of the disc is large as compared to the wavelength of the sound radiated into the fluid. Such a construction is desirable for production control applications where a more intense concentration of sound is required between the transmitting to the receiving transducers. An example of such an application is found in viscous liquids which have high attenuation to sound. There, it is necessary to increase the beam intensification of the sound to achieve good transmission through the viscous liquid.

FIGS. 5 and 6 illustrate another type of construction, which is basically similar to the construction shown in FIGS. 1 and 2. Again, the entire housing 101 may be machined from a single block of corrosion resistant material, such as stainless steel, for example. The housing 101 has a shape which is generally similar to the shape of the housing 10, with the exception that the sealed end has a solid nose section 102, within which is drilled an axial hole 103.

A somewhat cylindrical core support member 104 is used for aligning and locating the piezoelectric ceramic cylinder 105. This cylinder 105 and the previously described cylinder 14 are constructed in approximately the same manner and from approximately the same material. The ceramic cylinder 105 fits snugly over the outer surface of the support member 104.

On one end, the cylindrical support member 104 is provided with a pin-like extension tip 106 which fits into the hole 103. Three spacing members 124 are attached to the opposite end of the cylindrical support member 104. These spacing members locate the opposite end of the member 104 within a clearance diameter provided in the opening of the base portion of the housing member 101.

To further locate and stabilize the support member 104, three cylindrical strips 107 of silicone rubber, or other suitable heat resistant material, are employed as spacers for locating the inside surface of the ceramic cylinder 105, concentrically with respect to the outside diameter of the cylindrical support member 104; and, therefore, with respect to the inside of the housing 101. Conductor wires 108 and 109 are soldered to the electrode surfaces of the ceramic cylinder 105 before it is assembled over the spacers 107.

After completing the described assembly of the ceramic cylinder 105 and support member 104, the assembled structure is dropped into the housing 101. The entire mechanical structure becomes a perfectly aligned concentric assembly. After soldering the wires 108 and 109 to the electrical conductors 110 and 111 in the cable 112, a sound conducting high temperature resisting potting compound 113 is employed to complete the assembled structure in a manner which is similar to the structures illustrated in the other figures.

Other configurations of the housing structure and the transducer element may, of course, be used without departing from the basic teachings of this invention. For

example, in FIG. 3 the sound transparent housing wall 12 need not extend outward as a thimble-shaped tubular shell with a domed end. Instead, a flat thin wall might terminate the sealed end of the housing, and the disc 24 could be either spaced parallel to the flat end wall or cemented directly to the wall with a suitable high temperature adhesive, such as epoxy. Another modification uses X-cut quartz for the piezoelectric plate 23. Still further examples of modifications will be perceived by those who are skilled in the art.

This invention has been described in connection with three embodiments which have been chosen to illustrate the basic ideas; however, it will be obvious to those skilled in the art that numerous deviations are possible from the specific details shown. Therefore, the appended claims are to be construed to cover all equivalent structures.

We claim:

I. An electroacoustic transducer for operating at temperatures exceeding the temperature of boiling water, said transducer comprising a unitary housing structure of stainless steel having a cylindrical tubular wall section with an opening surrounded by threads at one end and a closed bottom at the other end with no open joints therebetween, an axial hole inside the end of said closed bottom, means comprising a cylindrical tubular transducer element for converting alternating electrical signals into mechanical vibrations, means comprising a cylindrical core support member having an outer diameter which fits loosely inside said cylindrical transducer element, positioning means comprising a pin-like extension tip on said core member fitting into said axial hole for locating said support member with its axis in alignment with the axis of said cylindrical tubular wall section of said housing member, spacer means for locating said cylindrical tubular transducer element in concentric relationship over the cylindrical'support member, electrical conductor means connected to said transducer element, and sound conducting coupling means filling the space between the vibratile cylindrical surface of said transducer element and the surrounding surface of said tubular wall section of said housing structure.

2. An electroacoustic transducer for operating at temperatures exceeding the temperature of boiling water, said transducer comprising a unitary housing structure having a cylindrical tubular wall section with an opening surrounded by threads at one end and a closed bottom at the other end with no open joints therebetween, an axial hole inside the end of said closed bottom, means comprising a cylindrical tubular transducer element for converting alternating electrical signals into mechanical vibrations, means comprising a cylindrical core support member having an outer diameter which fits loosely inside said cylindrical transducer element, positioning means; comprising apin-like extension tip on said core member fitting into said axial hole for locating said support member with its axis in alignment with the axis of said cylindrical tubular wall section of said housing member, spacer means for locating said cylindrical tubular transducer element in concentric relationship over the cylindrical support member, electrical conductor means connected to said transducer element, and sound conducting coupling means filling the space between the vibratile cylindrical surface of said transducer element and the surrounding surface of said tubular wall section of said housing structure.

3. The invention in claim 2 wherein the entire housing structure is a unitary one-piece construction.

4. The invention in claim 2 wherein said transducer element is a polarized ceramic cylinder.

5. The invention in claim 2 wherein said ceramic cylinder is lead zirconate-titanate.

6. The invention in claim 2 wherein said sound conducting coupling means is made ofa silicone base. 

1. An electroacoustic transducer for operating at temperatures exceeding the temperature of boiling water, said transducer comprising a unitary housing structure of stainless steel having a cylindrical tubular wall section with an opening surrounded by threads at one end and a closed bottom at the other end with no open joints therebetween, an axial hole inside the end of said closed bottom, means comprising a cylindrical tubular transducer element for converting alternating electrical signals into mechanical vibrations, means comprising a cylindrical core support member having an outer diameter which fits loosely inside said cylindrical transducer element, positioning means comprising a pin-like extension tip on said core member fitting into said axial hole for locating said support member with its axis in alignment with the axis of said cylindrical tubular wall section of said housing member, spacer means for locating said cylindrical tubular transducer element in concentric relationship over the cylindrical support member, electrical conductor means connected to said transducer element, and sound conducting coupling means filling the space between the vibratile cylindrical surface of said transducer element and the surrounding surface of said tubular wall section of said housing structure.
 2. An electroacoustic transducer for operating at temperatures exceeding the temperature of boiling water, said transducer comprising a unitary housing structure having a cylindrical tubular wall section with an opening surrounded by threads at one end and a closed bottom at the other end with no open joints therebetween, an axial hole inside the end of said closed bottom, means comprising a cylindrical tubular transducer element for converting alternating electrical signals into mechanical vibrationS, means comprising a cylindrical core support member having an outer diameter which fits loosely inside said cylindrical transducer element, positioning means comprising a pin-like extension tip on said core member fitting into said axial hole for locating said support member with its axis in alignment with the axis of said cylindrical tubular wall section of said housing member, spacer means for locating said cylindrical tubular transducer element in concentric relationship over the cylindrical support member, electrical conductor means connected to said transducer element, and sound conducting coupling means filling the space between the vibratile cylindrical surface of said transducer element and the surrounding surface of said tubular wall section of said housing structure.
 3. The invention in claim 2 wherein the entire housing structure is a unitary one-piece construction.
 4. The invention in claim 2 wherein said transducer element is a polarized ceramic cylinder.
 5. The invention in claim 2 wherein said ceramic cylinder is lead zirconate-titanate.
 6. The invention in claim 2 wherein said sound conducting coupling means is made of a silicone base. 